An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s-1?
The time taken by sound to travel from the source to the reflecting surface will be half of this time = 
= 1.5 seconds
We know that,
Speed =
342 = 
Distance = 342 × 1.5
= 513 m
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